1. Field of the Invention
This invention relates to a method for continuously producing 3,3xe2x80x2,5,5xe2x80x2-tetra-t-butyl-4,4xe2x80x2-biphenol, more specifically to a method for continuously producing 3,3xe2x80x2,5,5xe2x80x2-tetra-t-butyl-4,4xe2x80x2-biphenol, an intermediate product of industrially important 4,4xe2x80x2-biphenol as the raw material of thermostable engineering plastic at a high invert ratio by restricting the production of byproducts.
2. Description of the Related Art
A method for producing 3,3xe2x80x2,5,5xe2x80x2-tetra-t-butyl-4,4xe2x80x2-biphenol (hereinafter TBBP) having 2,6-di-t-butylphenol (hereinafter 26B) as raw material that is oxidized with oxygen containing gas under a presence of alkali catalyst has already been known. For example, one of the known methods produces 3,3xe2x80x2,5,5xe2x80x2-tetra-t-butyl-4,4xe2x80x2-diphenoquinone (hereinafter TBBPQ) by oxidizing/dimerizing 26B under the presence of alkali catalyst, then reducing or carrying out proton disproportionate reaction to form TBBP (see Japanese Patent Publication No. Hei 4-60457). Further, a method for producing TBBP with one step by oxidizing/coupling 26B (see Japanese Patent Publication No. Hei 6-74227) is also known. TBBP obtained by the above-mentioned methods is formed into 4,4xe2x80x2-biphenol by removing butyl therefrom.
Formula 1 
However, these known conventional methods for producing TBBP are the batch-type production method using a single reactor. Such batch-type production method may suit for a small size of TBBP production. However, for a mass production, the reaction vessel may need to be enlarged or plural reaction vessels have to be aligned by which the batch process is performed. In either case, it is associated with a disadvantage of poor cost efficiency and poor productivity.
Further, when 26B as the raw material is oxidized with oxygen containing gas under the presence of alkali catalyst, TBBP is mainly produced. Simultaneously, as by-product, diphenoquinone such as TBBPQ is also produced. If this reaction is carried out with a continuous reaction method, conversion ratio of 26B is reduced compared with the reaction by means of the batch type. Then, if the conversion ratio of 26B is increased up to the same level as that of the batch type, it creates a problem of byproduct, particularly, diphenoquinone such as TBBPQ causing discoloration to the obtained products.
Recently, there has been a high demand for the development of a method for continuously producing TBBP, that is an intermediate product of industrially important 4,4xe2x80x2-biphenol as the raw material of thermostable engineering plastic at a high invert ratio by restricting the production of byproducts. It is an object of the present invention to provide a method for continuously producing TBBP at a high selection ratio by restricting the product of byproducts by using and oxidizing/dimerizing the raw material 26B.
The present invention provides a method for continuously producing 3,3xe2x80x2,5,5xe2x80x2-tetra-t-butyl-4,4xe2x80x2-biphenol by oxidizing/dimerizing 2,6-di-t-butylphenol, comprising steps of supplying 2,6-di-t-butylphenol to a first reaction section of a reaction apparatus in which at least the first and second reaction sections are connected in series; supplying alkali catalyst to at last said first reaction section; distributing oxygen containing gas to each reaction section respectively; whereby a reaction mixture containing 3,3xe2x80x2,5,5xe2x80x2-tetra-t-butyl-4,4xe2x80x2-biphenol is obtained from the last reaction section.